Two enzymes in myelin and cells from the nervous system are the subject of the proposed studies. One enzyme, carbonic anhydrase, occurs in other subcellular fractions as well as in the myelin sheath. This enzyme will be purified from myelin and characterized and will also be measured in oligodendroglial plasma membranes and isolated axolemma, two membrane systems which are likely to be associated with myelin fractions. Because carbonic anhydrase is believed to take part in regulation of intracellular ions and water in the brain and is considered, on the basis of somewhat ambiguous data, to be a "glial" marker enzyme, its activity will be studied in detail also in isolated astrocytes, neurons, oligodendroglia andaxons. The possibility that myelin carbonic anhydrase is involved in removal of fluid during compaction of myelin sheath will be approached by a determination of the enzyme in myelin from a hypomyelinating mutant. The carbonic anhydrase in choroid plexus, whether tightly membrane-bound or extractable by salts, will also be studied with reference to participation in ion an fluid transport into the cerebrospinal fluid. The second enzyme, 2',3'-cyclic nucleotide-3'-phosphohydrolase (CNP), is considered a marker enzyme for myelin. Although loss of CNP activity occurs along with loss of myelin in MS plaques and other myelinotoxic conditions, the function of CNP remains unknown. We will explore under new conditions the hypothesis that CNP has ribonuclease activity, and will also attempt to inhibit the enzyme in vitro and in vivo in an effort to determine whether loss of CNP activity prevents myelination or results in demyelination.